Download notification: use new ChromeNotificationBuilder API for metrics.

This CL converts download notification to use new builder API which
support general notification metric recording, including:

Mobile.SystemNotification.Action.Click
Mobile.SystemNotification.Content.Click
Mobile.SystemNotification.Dismiss

TBR=dtrainor@chromium.org

Bug: 898269
Change-Id: I0a0634d9fc4bc52da2258e54dca0de7cdd3d4f09
Reviewed-on: https://chromium-review.googlesource.com/c/1433137
Commit-Queue: Xing Liu <xingliu@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#626268}
4 files changed